This is a pilot study to evaluate the safety and physiologic effects of ABT-627, an endothelian-A receptor blocker, in patients with symptomatic CHF (Class III). This drug will allow the investigators to study the actions of chronic antagonism of the endothelin A receptor, thus leading to an increased understanding of the pathophysiologic role of endothelin in the evolution of heart failure. This clinical trial has enrolled and completed the study of 2 subjects to date. Both subjects experienced no adverse events in relationship to the study drug. One patient experienced acute dyspnea upon discontinuation of the Swan Ganz catheter which resolved spontaneously within minutes of oxygen administration. Chest X-ray, ECG and blood gasses were all unremarkable. The subject remained in the CCU one extra day for observation. Hemodynamically the cardiac pressures and wedge pressure decreased as was expected without a systemic decrease in blood pressure.